Metal composite and method of producing the same

ABSTRACT

A metal composite is produced by rolling or adhering together a layer of heat-treatable aluminum-base alloy and a layer of precipitation-hardenable stainless steel alloy. The ferrous alloy layer is responsive to thermal treatment to precipitation harden that layer in a temperature range which is suitable for solution heat treatment of the aluminum-base alloy layer. The composite may be heated to within that range, and quenched, to produce a composite which is outstanding in its resistance to denting and penetration from high velocity impact.

United States Patent Barkman et al.

Related U.S. Application Data Division of Ser. Nos. 380,064, July 2, 1964, abandoned, and Ser. No. 656,946, July 28, 1967, abandoned.

[52] U.S. Cl. 148/127; 29/1962; 148/34 [51] Int. Cl C22c 41/02; C21c H00 [58] Field of Search 29/1962, 197; 148/1 1.5, 148/12.3, 127, 34, 142

[56] References Cited UNITED STATES PATENTS 2,171,040 8/1939 Merritt et al. 29/1962 2,390,023 11/1945 Wyche 148/12 2,908,073 10/1959 Dulin 29/l96.2 X

3,195,991 7/1965 Stern et al. 29/1962 3,210,840 10/1965 Ulam 29/l96.2

3,261,724 7/1966 Ulam 29/1962 3,268,369 8/1966 Haugen 29/1962 [451 May 20, 1975 3,300,838 1/1967 Slater et al 29/1962 3,352,005 11/1967 Avellone 29/1962 3,400,450 9/1968 Nock et a1. 29/1962 X 3,406,446 10/1968 Muldovan 29/1962 X OTHER PUBLICATIONS Metals Handbook, 1961 Ed., pages 484, 485, & 506 [Gpl l1].

Alcoa Aluminum Handbook, Aluminum Co. of America, Pittsburgh, Pa., 1955, page 127 [Gp l l l]. Monypenny, 3rd Ed., Published 1951, pgs. 139-142 [Gpl 11].

Primary Examiner-Lovell C. Attorney, Agent, or FirmCushman, Darby and Cushman [57] ABSTRACT A metal composite is produced by rolling or adhering together a layer of heat-treatable aluminum-base alloy and a layer of precipitation-hardenable stainless steel alloy. The ferrous alloy layer is responsive to thermal treatment to precipitation harden that layer in a temperature range which is suitable for solution heat treatment of the aluminum-base alloy layer. The composite may be heated to within that range, and quenched, to produce a composite which is outstanding in its resistance to denting and penetration from high velocity impact.

9 Claims, No Drawings METAL COMPOSITE AND METHOD OF PRODUCING THE SAME This is a division of applications Ser. No. 380,064 filed July 2, 1964, now abandoned and Ser. No. 656.946 filed July 28, 1967, now abandoned.

This invention relates to novel composites having both ferrous and aluminous metal components. More particularly, the invention concerns bonded composites of heat-treatable aluminum base alloys and precipitation-hardenable stainless steels of the semiaustenitic type, which composites possess high resistance to penetration.

Various composites of aluminum or aluminum alloys and ferrous metals. such as stainless steels, have found limited application in highway trailer and tank car bodies, railway rolling stock, automotive trim, cooking utensils, shielding panels and members.

In accordance with the present invention there are provided novel composites of aluminum base alloys and precipitation-hardenable ferrous alloys, which composites exhibit superior properties of resistance to denting and penetration, together with a high degree of structural strength. The novel composites of the invention are outstanding in their resistance to high velocity impact and thus are useful in applications in which such resistance is of importance.

Aluminum base alloys which may be advantageously employed in accordance with the invention include heat-treatable wrought alloys of the aluminum-copper or the aluminum-zinc-magnesium types, such as copper-bearing alloys 2014. 2017, 2024, and 2025, ranging in copper content from about 3.5% to about 5.0%, and zinc-bearing alloys such as 7075 and 7002. the strength of which is increased by solution heat treatment (8l0990F.) followed by quenching.

The aluminum base alloys may also be used when clad on at least one side with aluminum, for example alclad 2024 with a 2.5% or a 5% cladding.

Ferrous alloys which are advantageously employed in the composites of the invention include the heat treatable alloys of iron with chromium and nickel, or with nickel itself as the major alloying ingredient. Thus, there may be employed annealed conventional stainless steels of the 18 Cr-8 Ni type, designated as 302 and 304, or iron-nickel alloys containing about 8% to 10% nickel. The stainless steels may be used in the form of sheet or of mesh.

In accordance with the invention, it has been found that composites which include the precipitation hardenable stainless steels of the semiaustenitic type provide superior properties of penetration resistance.

These stainless steels are particularly adapted to bonding with aluminum alloys which are responsive to thermal treatment within approximately the same temperature range as the stainless steels themselves. Examples of precipitation hardenable stainless steels of the semiaustenitic type are the grades available commercially under the designations 177 PH and PH -7 Mo (Armco Steel Corp., Middletown, Ohio). Stainless 17-7 PH has 17% chromium, 7% nickel plus 1% aluminum to effect its precipitation hardening ability. The alloy is austenitic in the annealed condition, but is martensitic in the hardened condition. Alloy PH 157 M0 is similar to 177 PH but with 2% molybdenum replacing 2% of the chromium, resulting in improved elevated temperature properties. Both of these steels are susceptible to a thermal hardening treatment which may produce ultimate strengths up to 240,000 p.s.i. The alloys are available as sheet in the cold rolled or cold drawn condition (Condition C), which when subsequently aged at about 900F., develop high strength levels.

Typical analyses include: by weight) In the preparation of the composites of the invention, the sheets of aluminum and of stainless steel may be of any desired thickness compatible with good bonding, varying from foil gages up to the limit of the processing equipment. Preferred aluminum alloy gages vary, for example, from 0.040 inches to 0.125 inches, while suitable stainless steel gages may range from 0.004 inches to 0.016 inches, all before bonding. These gage ranges are to be considered as illustrative, however, and not as limiting.

The composites of the invention may be bonded by rolling or by means of suitable adhesives, but rolling is preferred. Bonding is advantageously performed by a rolling operation in which the stainless steel or ferrous alloy sheet is maintained substantially at room temperature. The aluminum alloy is preheated to a temperature between about 650F. and about 1000F., depending upon the alloy employed, care being taken to avoid grain boundary melting. A temperature range between about 850 and about 950F. ordinarily is preferred. The time of preheat may vary according to conditions, but generally a period of from 5 to 15 minutes is sufficient to uniformly heat the aluminum to the desired temperature. The time of preheat should, however, be kept to a minimum because of surface oxidation.

The metal-to-metal composites of the invention may be of the binary type, i.e. a single layer of aluminum alloy bonded to a single layer of ferrous alloy, or they may be of the sandwich type, such as a layer of aluminum alloy between two layers of stainless steel. Where alclad alloy is used, the steel is preferably bonded to the aluminum cladding layer. Also included within the scope of the invention are composites having adjacent multiple thicknesses of one or both of the ferrous and aluminous metal components.

There may also be included in the composite a layer of a plastic material capable of high elongation, for example, a layer of polyester, such as polyethylene terephthalate (Mylar), or of polypropylene, preferably biaxially oriented, or a composite of aluminum foil and plastic film, or a layer of a linear polyamide (nylon), preferably in the form of felt or woven fiber.

The composites may be bonded, particularly where a plastic layer is included, with a suitable adhesive, instead of being rolled. An example of such an adhesive is a mixture of 55% by weight of an epoxy resin (Armco No. 1009), and 45% by weight of a polysulfide polymer (Thiokol) obtained by the reaction of an alkali metal polysulfide with an organic dichloride.

In preparing the composites of the invention, the surface of the aluminum or aluminum base alloy is degreased, and is then roughened by wire brushing, sanding, grinding, or like methods, in order to remove any film of thin layer of aluminum oxide which would interfere with bonding. If desired, a chemical dip may also be employed. Similarly, the ferrous alloy is subjected to roughening by brushing, or grinding, to break up the oxide layer.

As mentioned previously, bonding may be by means of an adhesive or by rolling. Where rolling is used, the production of a bond may be effected with a reduction in the thickness of the aluminum alloy sheet from about 30% to about 70%, and in the stainless steel sheet from about 10% to about 50%. Rolling is carried out in conventional equipment, an overall gage reduction or about 50% resulting in satisfactory bonding.

After bonding, the composite is subjected, in accordance with the invention, to a thermal treatment by reheating the bonded composite to a temperature between about 850F. and about 950F. for a period of from about 15 minutes to about 1 hour. The temperature is selected according to the particular alloys involved. Thus, for example, alloy 2024 requires treatment at about 920F., while alloy 7075 is heated at about 880F. Followed by a cold water quench, such thermal treatment places the aluminum in T-4 temper condition, while if followed by a cold water quench and precipitation hardening (aging) it places the aluminum in T-6 temper condition. The treatment also accomplishes a hardening of the stainless steel, particularly if the steel used is in the aforementioned Condition C, thus completing the treatment of both the aluminum alloy and the steel.

With regard to resistance to penetration, the composites of the invention appear to exhibit a potentiating or synergistic effect, in that the resistance to penetration of the composite is greater than would be expected from the cumulative effect of the individual layers.

The following examples serve to illustrate the practice of the invention, but are not to be considered as limiting:

EXAMPLE 1 A composite was prepared from a sheet of annealed alclad 2024 alloy, clad on one side with aluminum, dimensions 10 inches X 16 inches X 0.080 inch, and a sheet of annealed stainless steel 17-7 PH, dimensions 12 inches X 16 inches X 0.016 inch. Prior to bonding, both pieces were wire brushed on the side to be bonded. The 2024 sheet was heated for 10 minutes at 900F., and the 17-7 PH sheet was maintained at room temperature. The sheets were bonded by rolling in a 4- high mill having work rolls 8 inches in diameter, backup rolls 16 inches, width 18 inches, using a mill setting of 0.015 inch (negative roll gap). The resulting 0.049 inch composite was heat treated at 920F. for 20 minutes and then quenched in cold water.

The composite exhibited longitudinally a tensile strength of 91,900 psi., a yield strength of 73,600 psi, an elongation in 2 inches of 10.0%, and a modulus of elasticity of 13.0 X 10 transversely, the values were: tensile strength 88,900 psi., yield strength 64,300 psi., elongation 11.5%, modulus of elasticity 13.0 X 10 EXAMPLE 2 Proceeding as in Example 1, a composite was prepared from a sheet of annealed alclad 2024 alloy, di-

mensions 10 inches X 16 inches X 0.080 inch, and a sheet of annealed 17-7 PH stainless steel, dimensions 12 inches X 16 inches X 0.008 inch. Both pieces were wire brushed on one side before bonding. Prior to bonding the 2024 sheet was heated to 900F. for 10 minutes, while the steel was kept at room temperature. Bonding was performed at a mill setting of 0.000 inch (zero roll gap). The composite (0.053 inch) was heat treated at 920F. for 20 minutes and then quenched in cold water.

The composite exhibited longitudinally a tensile strength of 58,100 psi., a yield strength of 33,600 psi, an elongation of 17.7% in 2 inches, and a modulus of elasticity of 12.0 X transversely the values were: tensile strength 58,100 psi, yield strength 32,000 psi, elongation 18.2%, same modulus.

EXAMPLE 3 Proceeding as in Example 1, a sandwich composite was prepared from two sheets of annealed alclad 2024 alloy, dimensions 10 inches X 16 inches X 0.040 inch, with an intermediate sheet of fully annealed stainless steel 17-7 PH, dimensions 12 inches X 16 inches X 0.008 inch, bonding being on the sides of the 2024 alloy having aluminum cladding. Both materials were wire brushed before bonding. Alloy 2024 pieces were heated for 10 minutes at 900F., while the steel was kept at room temperature. The roll bonding was carried out at a mill setting of 0.000 inch (zero roll gap). The composite (0.052 inch) was heat treated at 920F. for 20 minutes and quenched in cold water.

The composite exhibited longitudinal tensile strength of 69,500 psi, yield strength of 51,900 psi, elongation of 13.5%, and modulus of elasticity of 11.9 X 10 EXAMPLE 4 Proceeding as in Example 1, a composite was prepared by rolling a sheet of alclad 2024 alloy to a thickness of 0.080 inch, annealing for 650F. for 30 minutes, wire brushing the clad face of the 2024 sheet and a 0.004 inch thick sheet of stainless steel PH l5-7 Mo (full hard treated), heating the 2024 piece for 10 minutes at 850F., keeping the steel at room temperature, bonding the sheets by rolling (0.020 roll gap) into a composite of thickness 0.065 inch, heat treating at 920F. for 20 minutes, and finally quenching in cold water.

EXAMPLE 5 EXAMPLE 6 Proceeding as in Example 3, a composite sandwich was prepared from a core piece of 7075 aluminum alloy and two pieces of stainless steel l7-7 PH.

EXAMPLE 7 Proceeding as in Example 1, a sheet of alclad 2024 alloy was rolled to 0.125 inch thickness, annealed, and bonded to a piece of stainless steel l7-7 PH thickness 0.016 inch, the materials being rolled (mill setting of 0.020) to a thickness of 0.090 inch. The composite was heat treated and then rolled further to a final thickness of 0.065 inch.

EXAMPLE 8 Proceeding as in Example 7, another composite of aluminum alloy and stainless steel was produced by rolling (mill setting of 0.015) directly to a composite thickness of 0.065 inch, followed by heat treatment.

EXAMPLE 9 A composite was prepared as in Example 1, by joining a sheet of alclad 2024 alloy, thickness 0.080 inch, which was wire brushed, to a piece of fine stainless steel 304 mesh which had been previously etched with caustic soda, by rolling (0.020 gap setting) to a total thickness of 0.065 inches, followed by solution heat treatment of the aluminum alloy component.

While present preferred embodiments of the invention have been described, it will be appreciated that the invention may be otherwise variously embodied and practiced within the scope of the following claims.

We claim:

1. In the art of producing a metal composite having a layer of stainless steel and a layer of aluminous metal, the latter being a heat-treatable aluminum base alloy of the type adapted for solution heat treatment in the range of about 850950F., the improvement comprising:

providing a bonded composite of the aluminum alloy and a member of the class of semi-austenitic precipitation hardenable stainless steels which are susceptible to aging treatment at a temperature in said range of about 850-950F. effective to strengthen the steel;

heating the bonded composite in said temperature range for a period sufficient to effect solution treatment of the aluminum alloy component, thereby concurrently age hardening the stainless steel component; and

quenching the composite at a cooling rate sufficient to retain the aluminum alloys soluble constituents in solid solution.

2. The method of claim 1, including the step of bonding a layer of said aluminum-base alloy to a layer of precipitation-hardenable stainless steel alloy consisting essentially of l6.0l8.0% Cr; 6.507.75% Ni;

075-1 .50% Al; up to 0.09% C; up to 1.00% Mn; up to 0.03% S; up to 1.00% Si and balance substantially iron.

3. The method of claim 1, including the step of bonding a layer of said aluminum-base alloy to a layer of precipitation-hardenable stainless steel alloy consisting essentially of 14.0-16.0% Cr; 6.507.75% Ni; 0.75l.50% Al; 2.03.0% Mo; up to 0.09% C; up to 1.60% Mn; up to 0.03% S; up to 1.00% Si and balance substantially iron.

4. The method of claim 2 wherein the bonding step comprises bonding a layer of copper bearing, aluminum-base alloy 2024 to a layer of precipitationhardenable stainless steel alloy consisting essentially of approximately 17% chromium, 7% nickel and 1% aluminum, balance substantially iron.

5. The method of claim 3 wherein the bonding step comprises bonding a layer of zinc bearing, aluminumbase alloy 2024 to a layer of precipitation-hardenable stainless steel alloy consisting essentially of approximately 17% chromium, 7% nickel, and 1% aluminum, balance substantially iron.

6. The method of claim 3 wherein the bonding step comprises bonding a layer of copper bearing, aluminum-base alloy 2024 to a layer of precipitationhardenable stainless steel alloy consisting essentially of approximately 15% chromium, 7% nickel, 1% aluminum and 2% molybdenum, balance substantially iron.

7. The method of claim 3 wherein the bonding step comprises bonding a layer of zinc bearing, aluminumbase alloy 2024 to a layer of precipitation-hardenable stainless steel alloy consisting essentially of approximately 15% chromium, 7% nickel, 1% aluminum and 2% molybdenum, balance substantially iron.

8. The method of claim 1 wherein the bonded composite comprises a layer of aluminum-base alloy consisting essentially of up to 0.50% Si; up to 0.50% Fe; 3.84.9% Cu; 0.300.9% Mn; 1.21.8% Mg; up to 0.10% Cr; up to 0.25% Zn and balance substantially aluminum.

9. The method of claim 1 wherein the bonded composite comprises a layer of aluminum-base alloy consisting essentially of up to 0.50% Si; up to 0.7% Fe; l.22.0% Cu; up to 0.30% Mn; 2.l2.9% Mg; 0.18-0.40% Cr; 5.l-6.1% Zn; up to 0.20% Ti and balance substantially aluminum. 

1. IN THE ART OF PRODUCING A METAL COMPOSITE HAVING A LAYER OF STAINLESS AND A LAYER OF ALUMINUM METAL, THE LATTER BEING A HEAT-TREATABLE ALUMINUM BASE ALLOY OF THE TYPE ADAPTED FOR SOLUTION HEAT TREATMENT IN THE RANGE OF ABOUT 850*-950*F., THE IMPROVEMENT COMPRISING: PROVIDING A BONDED COMPOSITE OF THE ALUMINUM ALLOY AND A MEMBER OF THE CLASS OF SEMI-AUSTENITIC PRECIPITATION HARDENABLE STAINLES STEELS WHICH ARE SUSCEPTIBLE TO AGING TREATMENT AT A TEMPERATURE IN SAID RANGE OF ABOUT 850*-950*F. EFFECTIVE TO STRENGTHEN THE STEEL; HEATING THE BONDED COMPOSITE IN SAID TEMPERATURE RANGE FOR A PERIOD SUFFICIENT TO EFFECT SOLUTION TREATMENT OF THE ALUMINUM ALLOY COMPONENT, THEREBY CONCURRENTLY AGE HARDENING THE STAINLESS STEEL COMPONENT; AND QUENCHING THE COMPOSITE AT A COOLING RATE SUFFICIENT TO RETAIN THE ALUMINUM ALLOY''S SOLUBLE CONSTITUENTS IN SOLID SOLUTION.
 2. The method of claim 1, including the step of bonding a layer of said aluminum-base alloy to a layer of precipitation-hardenable stainless steel alloy consisting essentially of 16.0-18.0% Cr; 6.50-7.75% Ni; 0.75-1.50% Al; up to 0.09% C; up to 1.00% Mn; up to 0.03% S; up to 1.00% Si and balance substantially iron.
 3. The method of claim 1, including the step of bonding a layer of said aluminum-base alloy to a layer of precipitation-hardenable stainless steel alloy consisting essentially of 14.0-16.0% Cr; 6.50-7.75% Ni; 0.75-1.50% Al; 2.0-3.0% Mo; up to 0.09% C; up to 1.60% Mn; up to 0.03% S; up to 1.00% Si and balance substantially iron.
 4. The method of claim 2 wherein the bonding step comprises bonding a layer of copper bearing, aluminum-base alloy 2024 to a layer of precipitation-hardenable stainless steel alloy consisting essentially of approximately 17% chromium, 7% nickel and 1% aluminum, balance substantially iron.
 5. The method of claim 3 wherein the bonding step comprises bonding a layer of zinc bearing, aluminum-base alloy 2024 to a layer of precipitation-hardenable stainless steel alloy consisting essentially of approximately 17% chromium, 7% nickel, and 1% aluminum, balance substantially iron.
 6. The method of claim 3 wherein the bonding step comprises bonding a layer of copper bearing, aluminum-base alloy 2024 to a layer of precipitation-hardenable stainless steel alloy consisting essentially of approximately 15% chromium, 7% nickel, 1% aluminum and 2% molybdenum, balance substantially iron.
 7. The method of claim 3 wherein the bonding step comprises bonding a layer of zinc bearing, aluminum-base alloy 2024 to a layer of precipitation-hardenable stainless steel alloy consisting essentially of approximately 15% chromium, 7% nickel, 1% aluminum and 2% molybdenum, balance substantiaLly iron.
 8. The method of claim 1 wherein the bonded composite comprises a layer of aluminum-base alloy consisting essentially of up to 0.50% Si; up to 0.50% Fe; 3.8-4.9% Cu; 0.30-0.9% Mn; 1.2-1.8% Mg; up to 0.10% Cr; up to 0.25% Zn and balance substantially aluminum.
 9. The method of claim 1 wherein the bonded composite comprises a layer of aluminum-base alloy consisting essentially of up to 0.50% Si; up to 0.7% Fe; 1.2-2.0% Cu; up to 0.30% Mn; 2.1-2.9% Mg; 0.18-0.40% Cr; 5.1-6.1% Zn; up to 0.20% Ti and balance substantially aluminum. 